The present invention is directed to improvement of manufacturability of an article or product and/or reduction of manufacturing cost thereof. More specifically, the present invention is concerned with a method of quantitatively evaluating whether or not a designed structure of an article or product is easy to manufacture on the basis of relevant design information prepared or generated by using a computer-aided design system (hereinafter also referred to as the CAD processor in abbreviation), to thereby determine at an earlier stage of a design process a best or optimal design plan or plan and hence a best or optimal manufacturing or fabricating method from a plurality of design plans or plans inclusive of alternative proposals. The present invention is also concerned with a system for carrying out the method mentioned above.
Heretofore, there have been proposed a variety of evaluation methods which allows a design engineer to evaluate in a stage of a design procedure whether or not a product being designed has a structure easy to manufacture. According to a first method referred to as the design review method and adopted widely, the manufacturability (i.e., ease of manufacture) of an article or product as designed is determined by those skilled in the design, production, inspection and other techniques on the basis of their empirical knowledges or experiences, wherein those portions to be improved, if any, are pointed out by them. According to a second evaluation method also adopted generally, a process plan is created on the basis of a design drawing, and the costs involved in processability parts and/or assembling an article as designed as well as the time required therefor is estimated, whereon the expert engineer skilled in the technique for manufacturing the article or product of concern favorableness or satisfactoriness of the designed structure on the basis of the estimated values and his or her empirical knowledges. As third and fourth evaluation methods known heretofore, there can be mentioned those disclosed in an article entitled "KUMITATEYASUI SEKKEI (Design Easy To Implement)" and contained in "NIKKEI MECHANICAL" published Mar. 21, 1988, pp. 37-48.
According to the third method mentioned above, a part attaching process is analytically divided into several process elements, which are then imparted with respective evaluation scores determined in dependence on the degrees of easiness or difficulty in carrying out the process elements, wherein the processes required for attaching part are represented by the aforementioned process elements, and then assemblability (degree of susceptibility to assembling) of the article or product of concern as a whole is evaluated on the basis of the calculated totality of the evaluation scores imparted to the individual process elements while extracting those process elements which make the part attachments difficult.
In this conjunction, it should however be mentioned that there is contained in the article mentioned above neither teachings nor suggestions as to the method for assigning the evaluation scores, the method for totalization of the evaluation scores and others. Apparently, the design engineer determines an overall or synthetic optimality for a plural kinds or sorts of workabilities such as processability (degree of susceptibility to processing), assemblability (degree of susceptibility to assembling) and the like by relying on some means. However, in the case of the evaluation method mentioned above, the favorableness or satisfactoriness is decided rather intuitively without presenting definitely the ground for the decision.
According to the fourth method mentioned above, items to be checked are classified to alignability, positionability, chuckability, attachability and other features of parts are allocated with scores determined intuitively or empirically which represent degrees of easiness or difficulty of aligning, positioning, chucking, attaching and so forth of the parts. Upon evaluation of the assemblability of a given article as designed, the design engineer determines the presence or absence of the items for checking applicable to the article of concern and inputs them to the system, whereon the assemblability of the article as a whole is evaluated on the basis of a sum of the above-mentioned scores assigned to the selected items while those parts providing difficulty in assembling thereof are extracted. In conjunction with calculation for the totalization described above, it is reported in the article cited previously that for each of the individual parts, the scores mentioned above are subtracted or eliminated from the full mark of "100 points", whereon the total score for all the relevant check items is determined, and improvement of the design is performed until the mean value of the total scores of the individual parts attains at least seventy points.
At this juncture, it is also noted that JP-A-61-59900 discloses a method for design improvement which is applied to assembling of a printed substrate package and according to which evaluation scores are determined and displayed by resorting to a procedure similar to the fourth method described above.
The first mentioned prior art evaluation method is of a qualitative nature rather than quantitative and is disadvantageous in that not a little difficulty is encountered in expressing objectively and quantitatively to what extent the structure of an article or product under evaluation is favorable or unfavorable (satisfactory or unsatisfactory) for manufacturing or how effective the improvement as attempted will be. Besides, this method suffers from a problem that it can be carried out only by those having sufficient skilfullness in the design and manufacture engineering. According to the second mentioned prior art evaluation method, the assembling cost can certainly be estimated for an article or product as a whole or for every individual part or for some of the parts constituting the article. However, it is difficult to decide merely on the basis of only the assembling costs whether the designed structure is well qualified or whether any further improvement is necessary. Moreover, this known method has a drawback that the evaluation requires not a few experiences and knowledges as well as lots of time for the calculations involved therein, which makes the evaluation very difficult. Besides, unless the design of the article of concern has been completed, evaluation itself is rendered difficult. Consequently, improvement or modification of the design as found necessary can not be done until the design has been completed, which in turn means that an intolerable lot of time and expenditure will be taken for any further improvement of the design once completed. Under the circumstances, many articles designed rather unsatisfactorily or unfavorably have to be transferred to a production line without undergoing the further improvement, thus giving rise to a problem that the attempt for enhancing the productivity and reducing the cost often encounters an obstacle.
In brief, the first and second methods described above suffer from the shortcomings mentioned below.
(1) Evaluation is not quantitative but qualitative by nature, making impossible the quantitative evaluation.
(2) Evaluation can be made only by those having an abundance of experience or some knowledge of evaluation procedure. Further, the synthetic satisfactoriness of a decision for a plurality of different types of works or processes can not be made while presenting explicitly the ground therefor.
(3) With the evaluation based only on such factors as the attachment/assembling cost and/or the processing cost, it is difficult to decide whether the design is satisfactory or not.
(4) Enormous labor or time is required for the evaluation.
(5) Evaluation can be made only after the design has been completed or at some time point close to the completion of the design, which makes it difficult to improve the design after the evaluation.
(6) It is difficult to improve the article or parts because of difficulty in deciding the quality of design on the part-by-part basis.
With the third and fourth prior art methods described hereinbefore, it is contemplated to tackle or solve the problems enumerated above. The third prior art evaluation method certainly permits a time-sparing evaluation without need for rich experience. However, there arise such problems that relations between the evaluation indexes and the cost and time involved in the process are indefinite and that the cost and the result of the evaluation is difficult to verify because of lacking of a definite and concrete presentation of the engineering standards which are relied on in determining the relation between the evaluation index and the expenditure. Accordingly, it is ambiguous "what meaning a high evaluation score has", presenting thus a problem that it is impossible to decide with high accuracy whether the assemblability evaluation is of high qualification or reliability. Besides, since the evaluation is made on a process basis, it is difficult to specify those parts of an article which are poor in attachability.
The fourth prior art method described hereinbefore is also disadvantageous in that it is not clear whether a high or low evaluation score can really lead to low or high cost because of a lacking of presentation of the definite engineering standards for determining the relations between the evaluation indexes and the assembling costs. Besides, it is considered that a large number of items to be checked for the evaluation makes it difficult to execute the evaluation procedure.
The inventors of the present application have developed an assemblability evaluation method for evaluating quantitatively the degree of easiness of assembling, i.e., assemblability, and a processability evaluation method for evaluating the degree of ease of processing, i.e., processability, which are distinguished from the third and fourth methods described hereinbefore and already proposed as a manufacturability evaluation method for evaluating the degree of ease of manufacturing an object as designed on the basis of the results of the assemblability evaluation method and the processability evaluation method mentioned above. Reference may be made to "KIKAI SEKKEI (MACHINE DESIGNING)" published by Nikkan Kogyou Shinbun Company of Japan, Vol. 33, No. 7 (June, 1989), pp. 39-47.
More specifically, the proposal made by the inventors and disclosed in the above-mentioned literature is directed to a method of aiding a design engineer in making the decision quantitatively whether or not an article is easy to manufacture on the basis of a design plan of that article at an earlier stage of design process and a method of aiding the design engineer in proceeding with improvement of the design on the basis of the result of the evaluations made on the design plan presented for the evaluation.
According to the method now under consideration, works to be done in various manufacturing steps on individual parts constituting an article of concern are classified to basic elements and supplementary elements for each kind of works (e.g. for each of assembling work and processing work such as machining or the like), wherein information or data indicating works to be performed on the individual parts constituting the article under evaluation in terms of the relevant basic elements and the supplementary elements, respectively, is inputted to a system together with a command for making evaluation concerning the degree of easiness or difficulty of works involved in manufacturing the article of concern.
For carrying out the method under consideration, real values of the costs and the time involved in the various works actually done by combinations of given basic elements and supplementary elements, respectively, are inputted to the system for arithmetically determining in precedence the indexes (referred to as basic elimination scores and supplementary coefficients) indicating the workability or the degrees of ease of works to be performed on the individual parts on the basis of the basic elements and the supplementary elements, the results of which are stored in a database.
On the other hand, the system for carrying out the instant method is so arranged as to accept the evaluation request for groups of the basic elements, the supplementary elements and others for the article under evaluation as inputted by the analyzer, to thereby calculate the evaluation score indicating the workability of the article under evaluation (i.e., degree of easiness or difficulty of works involved in assembling, processing and/or manufacturing the article) by reference to the data stored in the database, the results of the calculation being outputted.
FIG. 1 of the accompanying drawings shows schematically an arrangement of the system mentioned above. A design engineer or analyzer 10 reads information required for evaluation from a drawing 11 or a sample 12 and inputs the information into a manufacturability evaluation system 14 via a keyboard 13, whereon the system 14 performs the evaluation on the basis of the information. The result of the evaluation is outputted through a printer 15. The analyzer 10 decides satisfactoriness of the manufacturing method of concern on the basis of the data as printed out. Design improvement, if necessary, is performed (step 16) and the information is fed back to a CAD processor 21.
Problems of the third and fourth methods as well as the method developed by the inventors of the present application (hereinafter referred to as the fifth method) are summarized below.
(1) In these methods, it is a prerequisite that the individual items for evaluation and the indexes indicating the degrees of ease of the works for the basic elements, the supplementary elements and the process elements representing the elements or components of a work have to be created in precedence and registered in the database. However, the method of creating the indexes as well as the relations between the indexes and the costs which can be known from the creating method are regarded as the know-how and not published.
(2) The analyzer has to specify a method of manufacturing an article which constitutes the object for the design and then selects or extracts the items for evaluation, the basic elements, the supplementary elements and the process elements for inputting them to the system together with a command for execution of the evaluation.
(3) It is a precondition that after the system has determined arithmetically the evaluation score representing the index indicating the manufacturability (degree of easiness or difficulty of manufacture) of an article as designed, the analyzer has to make a decision on the basis of the results outputted from the system as to satisfactoriness of the manufacturing method as well as the necessity or unnecessity of design improvement. Consequently, the step of decision made by the human being necessarily intervenes in feeding back the results of the evaluation to the CAD processor.
(4) None of the literatures introducing the prior art methods mentioned above discloses practically workable modes which enable these methods to be actually carried out.
(5) In the case of the fifth method, difficulty will be encountered in making decision on the basis of two evaluation indexes for the processability and the assemblability as to whether the design of concern is to be satisfactory or not, i.e, whether it is optimal for the manufacturing of the article of concern. Let's assume, by way of example, that there are presented to a design engineer a structuring model A improved in respect to the assemblability at the expense of processability because of primary reliance on the assemblability evaluation method and a structuring model B improved in the processability at the expense of the assemblability by relying primarily on the processability evaluation method, as is illustrated in FIG. 20 of the accompanying drawings. In such situation, the design engineer will not be able to make decision straightforwardly as to which of the model A or B should be adopted.